The standard inorganic styles of LEDs can come in many different varieties. These include different packages and configurations.

The variety of packages and styles enables them to be used in many different applications and in many different ways.

Also the different configurations of LEDs enable them to be used in many different ways - as indicators, as displays and as monitors.

LED configurations

There are a number of different formations or configurations that LEDs in which LEDs can be obtained:

Single colour: This is the standard format or configuration for an LED. It has two leads, one a cathode and the other an anode. The LED comes on and off according to when a current is passed through the diode.

Bi-colour LEDs : This format for LEDs uses a pair of LEDs wired in an inverse parallel formation. This enables one LED to be illuminated at a time dependent upon the polarity of the voltage applied.

LEDs do not withstand significant reverse voltages. Although the diodes in this configuration will experience a reverse bias, this is limited to the forward voltage of the other diode, and this is not sufficient to damage the reverse biased diode.

Tri-colour LEDs : This LED configuration again uses two separate LEDs, but in a different configuration. Each LED has a different colour. There are two anode connections and a single cathode. It is therefore possible to turn each LED on separately, giving a choice of two colours - the third is provided by turning both LEDs on together and giving a third colour by addition. It is also possible to have different intensities of both LEDs to further vary the colour.

Flashing LEDs: This form of LED is relatively easy to implement. The package contains not only the LED but also a simple IC that provides a timing function to enable the LED to flash.

Traditional LED packages

The traditional LED has been available since the early 1960s and has been produced in quantities of billions.

Typical LED package

LEDs are available in a variety of package sizes. Possibly the most widely used is the 5mm diameter one, although a host of others are available ranging from 1.8mm, 3mm, 4mm, 8mm, and 20mm. There are also and rectangular LEDs available - almost any size to fir a wide variety of requirements.

Surface mount, SMT LED packages

Like all components, LEDs are used in vast quantities in LED SMT packages. They are available in the industry outline packages. However they have not been subject to quite the same level of miniaturisation as many components such as resistors and capacitors that are available in 0201, etc. This is partly because they need to be a certain size to see!

The most common LED SMT sizes with dimensions are given below.

Packagedesignator

Length (mm)

Width (mm)

Height (mm)

1206

3.2

1.5

1.1

0805

2.0

1.25

0.8

0603

1.6

0.8

0.6

0402

1.0

0.5

0.45

LED displays

Although liquid crystal and other forms of display have taken over many alphanumeric display applications, LED technology is still used in a number of applications. It has advantages that it does not need external light as in the case of an LCD. However they are less versatile and costs for customisation normally prohibit this type of use. It is often only possible to display numeric characters, and sometimes some limited graphics

Nevertheless LED displays are used in many areas, particularly where power is not an issue. Alarm clocks, test instrumentation, and other forms of mains powered electronic apparatus use LED alphanumeric displays.

The LED alphanumeric displays use a variety of approaches to display the characters:

Seven segment: This form of display can be used to create digiots between "0" and "9". An additional LED can also provide a decimal point, making this basic form of LED display applicable for a variety of basic numeric display applications. One example may be clock radios where power is not an issue.

Star-burst: The starburst format for an LED display has the ability to illuminate fifteen lines and in this way it gives a considerable improvement in flexibility over that of the basic seven segment display. It can be programmed to create numeric characters as well as certain limited graphics.

Dot matrix: The dot matrix display is the most flexible format. The LED dot matrix display is made up from a matrix of LEDs, each providing a dot. It can be obtained in a variety of formats although 5 rows and five columns, or 7 rows and five columns are common formats.

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